Monday, October 22, 2012

Better Point-and-Shoot Shots with an External Flash

Last weekend, one of our friends celebrated their daughter's birthday party.  On this kind of occasion, I don't usually bring a DSLR anymore - I feel it is a little too much when we're not the celebrants.  Instead, I brought our trusty Lumix LX5 (reviewed here).  However, to get the best image quality out of the LX5, I paired it with an external flash, the Yongnuo YN-560EX (reviewed here).

Yes, the 560EX is a manual not TTL flash.  (I don't have a dedicated TTL flash for the Lumix LX5.)  However, using a manual flash while shooting run-and-gun is actually easier than it sounds.  (See: Therapy for TTL Addiction: How to Use Manual Flash).

In this post, I'll discuss my thought process in setting the flash and ambient exposures.

The birthday party was at a My Gym play area.  The room was about 4 or 5 times as long as it was wide.  The ceilings were white, and about 12 to 15 feet high.  One side of the room had mirrors while the other side had a mural and colorful playsets.
Not the same party but the same location, showing the ceiling
The first thing I do is assess the ambient light.  The party was late in the afternoon, almost sunset.  The storefront windows were covered by blinds to prevent glare.  There were fluorescent lights all over the ceiling, so the ambient light from the ceiling was soft.  Direct sunlight was streaming through and illuminating part of the room.  The direct sunlight was of course hard but it was coming in at an angle, so at least it had an interesting direction.

One possibility is to use ambient only.  There were two issues with this.  First, the fluorescent would be too dim, forcing the LX5 to struggle with much higher ISOs.  Second, there would be strong contrast between the sunlight and the fluorescent-lit areas.  Flash was definitely a useful tool under these circumstances.

Since I've decided that flash would help, the next thing is to figure out the respective roles of the ambient and flash.  One option is to expose for the ambient then use flash as fill.  It would solve the contrast between sunlit and fluorescent-lit areas.  However, it would not fix the dim fluorescent light (I would have to use high ISO).

On the opposite extreme, I could use flash only with no ambient, for maximum control.  The LX5 has an unlimited sync speed which facilitates 'deleting' the ambient.  But in this case, the subjects and the rest of the room were evenly lit with the ambient.  If I deleted the ambient for the subject, I would also be deleting the ambient for the room.  If I did that and used flash on the subject, then it would look artificial, like this (one of my early flash photos):
11 pictures for you

Or I would have to simulate the light in the room, which would have required at least a couple more flashes given the size of the room.  Not practical.

The compromise here is to use flash as the dominant light source, but to allow enough ambient to look natural.  How much ambient to allow here depends on a number of factors, such as: does the ambient look good or not, how consistent are the ambient and the flash, etc.  In this case, the ambient was fine (it's soft, comes from a reasonable direction, has a reasonable color, is consistent with the flash).  The more ambient I allowed, the more natural the image looked and the less the flash would have to work.  But because the camera can't handle high ISOs, I had to allow as much ambient as the camera could handle competently then use the flash for the rest.

I used manual exposure for the ambient.  In this case, I used the highest ISO the camera could manage, the widest available aperture, and used the slowest shutter speed that would not result in blur.  In the case of the LX5, I chose 400 ISO.  As for aperture, the LX5 can go as wide as f/2.0 to f/3.3 depending on the zoom; DOF is not really an issue for point and shoot.  For the shutter speed, I tried 1/100 first but it was too slow to get sharp enough shots of the kids.  So I tried progressively faster shutter speeds.  Of course it would be nice to shoot at 1/500 for sharpness but again, there would not be enough ambient in that case.  I settled at 1/200.

The rest of the exposure was lifted by the flash.  I wanted the flash to blend with the ambient - soft, overhead, white.  The logical choice was to bounce the flash against the ceiling.  That's exactly what I did, although I varied it slightly from pointing just straight up.  I also made sure to shield the flash with my hand so it wouldn't shine directly on the subjects.  In terms of intensity I just chimped it to lift the underexposed ambient to the right level.  That was around 1/4 power at 105mm zoom, although I was adjusting it up and down from time to time.

An alternative approach was to use automatic exposure, underexposed -1EV.  Closer to 0EV would be natural but again, the ambient was too dim -- plus shutter speed may be too slow).  I used aperture priority then chose the widest available aperture (again, DOF is not an issue for p&s), then I used flash to bring up the rest.  It's a simpler approach but with less control over the variables.

You recall that one of the issues is the contrast between the sunlit area and the fluorescent-lit area.  For those parts, the exposure was set for ambient, and the flash acted only as fill.
Aperture priority, 0EV.  No flash.

Aperture priority, 0EV. Flash added.

One of the activities at the party was riding a zipline.  To capture that, I used intentional flash blur.  I set the exposure to a slow enough shutter speed.  Then, because the subject would be moving and the LX5 isn't fast enough to focus continuously, I used a narrower aperture to get a deep DOF.  Then I used the ISO to bring the exposure up to around normal.  Given that the aperture was somewhat narrow and the ISO on the low side, I set the flash to full power, then tweaked ISO upward as needed to get the desired exposure.

Here are a few more shots from the party.